They're super persistent (especially when tennis balls are involved).

They can help their visually impaired owners graduate.

Having a dog means less having to go to the doctor.

"Medical research supports that statement. In 1980, a group of doctors followed 92 people for a year after the subjects were admitted to a coronary care unit. The mortality rate among animal owners was only 6 percent, while that of their pet-less counterparts was 28 percent."

Even when they're guilty of something, they still manage to look cute.

They have simple goals in life.

Their big floppy ears!

They can help with depression.

"Studies show that animals can reduce tension and improve mood. Along with treatment, pets can help some people with mild to moderate depression feel better. If you're depressed, here's a rundown of how pets could help."

They make excellent crime fighters.

Seriously.

They love stuffed animals just like we do.

They're great handshakers.

They can detect cancer in humans.

A dog named who lives with Dr. Hideto Sonoda from Fukuoka Dental College Hospital in Japan has this special talent. Marine, a 8-year-old black Labrador retriever, detected colorectal cancer 91 percent of the time when sniffing patients' breath.